The present invention relates to a technique for conducting die-bonding and wire-bonding operations while supporting a circuit-bearing surface of a semiconductor integrated circuit chip in a die-bonding process as well as in a wire-bonding process for the semiconductor integrated circuit chip, and more specifically concerns a jig used for assembling semiconductor devices which is capable of reducing damages to the circuit-bearing surface of the semiconductor integrated circuit chip and a manufacturing method for semiconductor devices wherein such a jig is used.
In general, semiconductor integrated circuit chips (hereinafter, referred to as xe2x80x9cchipsxe2x80x9d) are produced as follows: First, a chip is die-bonded onto a die pad of a lead frame through Ag paste, and after the Ag paste has been cured, bonding pads, formed on the chip, are wire-bonded to inner leads of the lead frame by the use of bonding wire or other members. After having sealed these with sealing materials such as resins and ceramics, tie bars and side bars are cut off, and outer leads are bent into desired shapes; thus, the chip is completed.
In recent years, there have been increasing demands for high-density, thin ICs, and in order to meet these demands, there have been proposed ICs wherein chips are bonded on both the back and surface sides of a lead frame. As shown in FIG. 8(a), in a die-bonding operation and a wire-bonding operation of such chips, the first chip 24a is die-bonded by a bonding collet 29 onto a die pad 23a on the first-surface side of a lead frame 22 that has been mounted on a support stage 25, in the same manner as the normal process, and the Ag paste is cured.
Next, as shown in FIGS. 8(b) through 8(d), the chip 24a is clamped by a heater block 30 and a clamp plate 31, and is fixed by applying a vacuum suction onto the back surface of the first-surface side die pad 23a through a suction hole 32. Then, while applying heat, the bonding pads of the first chip 24a and the inner leads on the first-surface side of the lead frame 22 are wire-bonded to each other through bonding wires 26.
Then, the lead frame 22 is turned over to be upside down, and as shown in FIG. 8(e), the second IC chip 24b is die-bonded onto a die pad 23b on the second-surface side of the lead frame 22 that has been mounted on a support stage 45 by using a bonding collet 29. The support stage 45 has a groove section 28a that is provided for preventing the first chip 24a that has been subjected to the die-bonding and wire-bonding from contacting the bonding wires 26, an inner section 45a for supporting the surface of the first chip 24a, and an outer section 45b for supporting the lead frame 22.
As shown in FIGS. 8(f), 8(g) and 8(h), after the Ag paste has been cured, this is clamped by a heater block 50 and the clamp plate 31. The heater block 50 has a groove section 28b that is provided for preventing the first chip 24a that has been subjected to the die-bonding and wire-bonding from contacting the bonding wires 26, an inner section 50a for supporting the surface of the first chip 24a, a suction hole 52 that is formed in the inner section 50a, and an outer section 50b for supporting the lead frame 22. Then, while applying a vacuum suction onto the surface of the first chip 24a through the suction hole 52 so as to fix the chip therein, as well an applying heat, the bonding pads on the surface of the second chip 24b and the inner leads of the lead frame 22 are wire-bonded to each other through bonding wires 26.
After having sealed the first chip 24a and the second chip 24b with sealing materials such as resins and ceramics at the same time, tie bars and side bars are cut off, and outer leads are bent into desired shapes; thus, the product is completed.
Moreover, another method has been proposed by Japanese Patent Publication No. 121462/1993 (Tokukaihei 5-121462).
After the first chip has been die-bonded onto a die pad on the first-surface side of a lead frame and the Ag paste has been cured, inner leads on the first-surface side and the bonding pads of the first chip are wire-bonded to each other through bonding wires, and only the inner leads on the first-surface side and the first chip are subjected to a resin-sealing process beforehand.
Next, the lead frame is turned over to be upside down, and after the second chip has been die-bonded onto the second-surface side of the lead frame and the Ag paste has been cured, inner leads on the second-surface side and the bonding pads of the second chip are wire-bonded to each other through bonding wires, and then the inner leads on the second-surface side of the lead frame and the second chip are subjected to a resin-sealing process.
In these methods, however, when the die-bonding operation and the wire-bonding operation are carried out on the second chip 24b of the lead frame 22, the circuit-bearing surface of the first chip 24a of the lead frame 22 needs to be contacted and supported by the inner section 45a of the support stage 45 and the inner section 50a of the heater block 50; this causes a pressure onto the circuit-bearing surface, resulting in the following problems.
Here, FIGS. 9(a) and 9(b), which explain a principle as to how cracks develop in a passivation film 33 during the forming process by the die-bonding and wire-bonding jig used in the conventional technique, are enlarged drawings, each of which shows a contacting and supporting section between the circuit-bearing surface of the first chip 24a of the lead frame 22 and the surface of the inner section 45a of the support stage 45 or the surface of the inner section 50a of the heater block 50.
As shown in FIG. 9(a), the passivation film 33 having a film-thickness of approximately 1 xcexcm is coated on the circuit-bearing surface of the first chip 24a, and serves an a final protective film. Here, it is actually inevitable to have minute protrusions and recessions on the surface of the inner section 45a of the support stage 45 (hereinafter, referred to as xe2x80x9cthe first supporting facexe2x80x9d) as well as on the surface of the inner section 50a of the heater block 50 (hereinafter, referred to as xe2x80x9cthe second supporting facexe2x80x9d) due to their machining processes, and the biggest protrusion 35, located thereon, partially comes into contact with the passivation film 33. As a result, a die-bonding load as well as a wire-bonding load is locally applied onto the passivation film 33, and this tends to cause a crack 36 due to concentration of stress.
Moreover, as shown in FIG. 9(b), if there is foreign matter, such as silicone fragments, having a comparatively high hardness and having sharp shapes between the passivation film 33 and the first supporting face or the second supporting face, the biggest foreign matter 34, located thereon, partially comes into contact with the passivation film 33. As a result, a die-bonding load as well as a wire-bonding load is locally applied onto the passivation film 33, and this tends to cause a crack 36 due to concentration of stress.
Here, the concentration of stress, which forms a main cause of the crack 36, is caused and developed mainly due to the fact that the first supporting face and the second supporting face are made of a rigid material such as a metallic material of iron group.
Cracks caused in the passivation film tend to reduce the humidity resistance of the chip, and those chips containing cracks tend to be extracted as defective ones during electrical-characteristic tests and reliability tests that are carried out after they have been sealed with resin; this results in a reduction in the final yield of the chips.
Furthers in the method of the above-mentioned Japanese Patent Publication No. 121462/1993 (Tokukaihei 5-121462), those processes, such as die-bonding, Ag-paste curing, wire-bonding and resin-sealing processes, need to be carried out on the first surface of the lead frame; this requires two times of resin-sealing processes in a separated manner, resulting in an increase in the number of the processes. Moreover, when die-bonding and wire-bonding operations are conducted on the second surface of a lead frame whose first surface has already been subjected to the resin-sealing process, the resin sealing the first surface tends to become a source of contamination, thereby giving adverse effects on the working environment wherein the die-bonding and wire-bonding operations are carried out.
The objective of the present invention is to provide a means for preventing cracks that tend to be caused in a passivation film that is coated on the circuit-bearing surface on the first chip that has already been die-bonded and wire-bonded onto the first surface of a lead frame, when the second chip is die-bonded and wire-bonded onto the second surface of the lead frame, and thereby for improving the reliability of the chips as well as the final yield there of.
In order to achieve the above-mentioned objective, the Jig used for assembling semiconductor devices of the present invention is provided with a rigid member for supporting a lead frame to which the first semiconductor integrated circuit chip has been bonded on its one surface from said surface side, and an elastic member for supporting the semiconductor integrated circuit chip from said surface side. With this arrangement, when the second semiconductor integrated circuit chip is die-bonded and wire-bonded onto the other surface of the lead frame, the elastic member makes it possible to alleviate concentration of stress that is applied onto the passivation film on the circuit-bearing surface of the first semiconductor integrated circuit chip through its elastic deformation. Consequently, it becomes possible to prevent cracks that are caused In the passivation film, and also to improve the reliability of semiconductor devices. Moreover, it is possible to improve the final yield after all the manufacturing processes.
Further, when the elastic member is arranged to contact the first semiconductor integrated circuit chip at its inner side than the wire-bonding member, it becomes possible to prevent the elastic member from unnecessarily intervening the wire-bonding member.
Moreover, when the elastic member is designed to have a ring shape, it becomes possible to reduce the contact area between the passivation film and the elastic member and also to allow the elastic member to be easily maintained at a predetermined position. Furthermore, when the elastic member is designed to have a round shape or an elliptic shape in its cross-member, it becomes possible to further reduce the contact area between the passivation film and the elastic member. Here, as for materials for the elastic member, it is preferable to use those materials that have elasticity to a bonding load that is applied by the bonding collet.
Furthermore, the rigid member may be designed so that it has an outer section for supporting a lead frame and an inner section that is formed to have a height lower than that of the elastic member, that is, to be located at a position corresponding to a lower part of the first semiconductor integrated circuit chip with the outer section supporting the lead frame to which the first semiconductor integrated circuit chip has been bonded, and so that the ring-shaped elastic member is fit to the inner section. With this arrangement, the elastic member is able to prevent the lead frame from contacting the inner section that is one portion of the rigid member. As a result, it is possible to prevent cracks that may be caused in the passivation film due to minute protrusions that are located on the rigid member. Further, even if foreign matter, such as silicone fragments, exist between the circuit-bearing surface of the first semiconductor integrated circuit chip and the rigid member, it is possible to alleviate concentration of stress that is applied onto the passivation film on the circuit-bearing surface of the first semiconductor integrated circuit chip through its elastic deformation, thereby making it possible to prevent cracks that may be caused in the passivation film.
In order to achieve the above-mentioned objective, another jig used for assembling semiconductor devices of the present invention is provided with a supporting section for supporting a lead frame to which the first semiconductor integrated circuit chip has been die-bonded and wire-bonded on its one surface while the second semiconductor integrated circuit chip has been die-bonded on the other surface, a clamp plate for pressing the lead frame onto the supporting section, and wire-bonding tools, such as a capillary, for wire-bonding the second semiconductor integrated circuit chip onto the lead frame. Here, the supporting section is characterized by including a rigid member for supporting the lead frame and an elastic member for supporting the first semiconductor integrated circuit chip. In this arrangement, when the second semiconductor integrated circuit chip is wire-bonded onto the lead frame, the circuit-bearing surface of the second semiconductor integrated circuit chip is supported by the elastic member. As a result, it becomes possible to prevent cracks that may be caused in the passivation film on the circuit-bearing surface due to contact with minute protrusions located on the rigid member, concentration of stress caused by foreign matters such as silicone fragments, and other phenomena.
Moreover, in a modified arrangement which features that the rigid member of the supporting section is made of a thermal conductive material having a high thermal conductivity, that the inner section of the rigid member has a hole that penetrates it in the vertical direction, and that the jig used for assembling semiconductor devices has a suction device for sucking air through the hole in the inner section of the rigid member and for making the lead frame adhere to the supporting section, it becomes possible to effectively transmit heat from the heating means to the bonding pads of the second semiconductor integrated circuit chip during the heating process in which the second semiconductor integrated circuit chip is wire-bonded to the lead frame.
In this case, as for materials for the elastic member, it is preferable to use those materials that have elasticity to a resultant force between a wire-bonding load exerted by the capillary and a suction force due to the suction device and also have resistance to heat that is applied by the heating means.
Furthermore, in the case of packaging semiconductor integrated circuit chips on both sides of a lead frame by using the above-mentioned jig used for assembling semiconductor devices, it is preferable to form a protective resin film on the circuit-bearing surface of a semiconductor integrated circuit chip at least within an area that comes into contact with the elastic member. Thus, while the lead frame, which has a semiconductor integrated circuit chip die-bonded on at least one surface thereof, is supported by the jig used for assembling semiconductor devices with the protective resin film and the elastic member being kept in contact with each other, the other semiconductor integrated circuit chip is packaged onto the surface of the lead frame opposite to the surface that is supported by the jig used for assembling semiconductor devices. Even if foreign matter such as silicone fragments, which have a comparatively high hardness and sharp shapes, exist between the supporting face of the elastic member of the jig used for assembling semiconductor devices and the semiconductor integrated circuit chip, this packaging method makes it possible to further absorb and alleviate the concentration of stress onto the circuit-bearing surface (passivation film) of the semiconductor Integrated circuit chip through the elastic deformation of the elastic member and the dumping function of the protective resin film. As a result, it becomes possible to prevent cracks that might be caused on the circuit-bearing surface of the semiconductor integrated circuit chip and also to improve the reliability of semiconductor devices. It is also possible to improve the final yield of semiconductor devices in the manufacturing process.
When the semiconductor integrated circuit chip that is coated with the protective resin film is used, it is preferable to take the following steps: First, a semiconductor integrated circuit chip is die-bonded onto one surface of a lead frame. After completion of a wire-bonding process on the semiconductor integrated circuit chip, the lead frame is turned over to be upside down, and while the lead frame la being supported by the aforementioned jig used for assembling semiconductor devices, a semiconductor integrated circuit chip is die-bonded onto the other surface of the lead frame. Then, the semiconductor integrated circuit chip is subject to a wire-bonding operation. With this packaging method, it is only necessary to form the protective resin film on one of the semiconductor integrated circuit chips that is to be first die-bonded onto the lead frame; this makes it possible to minimize the cost of material for the protective resin film.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.